This invention relates to thrust generating engines of the fluid expansion type for propelling a body through a fluid medium such as sea water and more particularly to underwater propulsion engines for torpedoes as disclosed in my prior U.S. Pat. No. 3,783,814, issued Jan. 8, 1974.
The foregoing type of propulsion engine involves the acceleration of water during passage through channels in the engine rotor. The inlet ends of the channels are opened and closed in response to rotation of the engine rotor, such rotation being induced by flow of the water along the helical paths of the channels to control cyclic intake into, filling of and outflow of the water from the channels. A pressurized propellant gas is injected into the inlet ends of the channels to accelerate the columns of water in the channels toward the exit ends. Expansion of the propellant gas at the inlet ends of the channels induces said acceleration of the water and resulting axial propelling thrust during its outflow from the exit ends of the channels.
Practical underwater applications of the foregoing type of propulsion engines are associated with a source of hot propellant gas. During injection of the gas into the engine channels, it was discovered that rapid cooling of the gas occurs with resultant high loss of energy to substantially offset the otherwise advantageous attributes of the engine. Such rapid cooling rate could not heretofore be explained by heat transfer through the gas-water interface adjacent to the inlet ends of the rotor channels. It is known that cavitation bubbles will form at the inlet ends of the channels when the water inflow is cut off. Such cavitation bubbles become attached to the flow blocking section of the engine body and the propellant gas has heretofore been injected into the bubble cavities. Apparently, rarefaction wave flow from the cavitation bubbles into the enclosing water mass causes the water to accelerate toward such bubbles and breaks the water up into many smaller bubbles or droplets, thereby increasing the interface surface area and the cooling rate.
It is therefore an important object of the present invention to substantially reduce the cooling rate of hot propellant gas injected into the columns of fluid medium filling the channels of an expansion thrust engine, whereby engine operation may be achieved with greater efficiency.
An additional object of the invention in accordance with the foregoing object is to reduce the cooling rate of hot propellant gas within the channels of an underwater propulsion engine by reducing water foaming activity during injection of such gas into the channels.